I agree with WDID's analysis of your sitch. Yes, the gall of him to ask for your permission and promise (because that's what it is, let me do this and pls don't make a huge fuss) and then to say that he doesn't want the OW to get into trouble with work or with his family?!?
You are a better woman than me for keeping your cool, I'll tell you that.
I think your H needs a really really good IC right away. He is throwing himself into the deep end and he doesn't even know it! He thinks his life would be better after getting involved with OW because of all the endorphins! You saw it coming, you saw that they were getting too close, you kept close tabs but he still left.
You know, I did what WDID suggested exactly. But it didn't help in my sitch but your H is a different person, it might help you. I think your H doesn't really know what he wants, he is looking hard for happiness but at all the wrong places. See if you can get him some help before messing up his life even more.
Me:39 H:40 S:9 D:7 First Bomb ONS:June 07 Second Bomb OW: March 08 Separated: March 08 M:15 yrs T:18 yrs H deep into A with OW Achieved ACCEPTANCE May 30, 09